How to make objects follow armature bone shape? (images included)
Looks like you have weighting wrong: delete the armature modifier you have created, select the paper, then the armature, then Ctrl P and choose "with EMPTY GROUPS option".
This option will create 3 empty vertex group with the same name of the three bones,  that can be manually weighted:
select the paper and enter in edit mode
select the vertex group tab in the properties window, select the first bone, select all the vertices around the first portion of the plane and click assign.
Do the same with the others two bones/portions of plane.

Done.